The cycle repeats when the carbon stored in the atmosphere as carbon dioxide gas is taken in.
the animal releases the carbon dioxide back into the atmosphere during respiration.
the animal eats a plant and uses its carbohydrates for energy.

Order of the cycle:

Step -1>>>>Step -4 >>>> Step -3 >>>>> step -2.

Explanation:

Step -1:

Carbon dioxide is taken in by plants during photosynthesis.

Step -4;

The animal eats a plant and uses its carbohydrates for energy.

Step - 3

The animal releases the carbon dioxide back into the atmosphere during respiration.

Step -2

The cycle repeats when the carbon stored in the atmosphere as carbon dioxide gas is taken in.

Therefore, order of the cycle is Step -1>>>>Step -4 >>>> Step -3 >>>>> step -2.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.